A shock to the dollar more like 1990 than the 1970s
The weakness in the U.S. dollar has often been cited as a main reason behind the spike in oil prices this year, but some market observers are getting increasingly worried over the potential harm rising oil could do to the greenback.
Long-term evidence suggests that oil and the Dollar Index have shown a strong negative correlation at about 0.7. In other words, as oil prices rise, the dollar would fall and vice versa. The logic behind this is simple: as oil rises, consumers scale back spending, therefore slowing down the economy and leading to lower interest rates and a depreciating currency. 
This inverse relationship didn’t hold in previous oil shocks, said Kathy Lien, chief strategist at DailyFX.com. But, she said, the current problems in the U.S. economy have made the dollar more vulnerable to downside risks.
There were three occasions over the past half century when oil prices spiked abruptly.
In 1973, oil jumped 134% after members of the then OAPEC (OPEC plus Egypt and Syria) announced that they were no longer exporting oil to nations that supported Israel in conflict with Syria and Egypt – a move that effectively shut down exports to the U.S., Western Europe and Japan.
In 1979, the price of crude oil soared 118% between January and December, with many analysts attributing the spike to the Iranian revolution and a gasoline shortage.
In both cases, the trade-weighted U.S. Dollar Index, which measures the greenback against a basket of the world’s major currencies, initially rallied along with oil as the Federal Reserve hiked interest rates to combat inflation, then sold off as growth contracted.
But the dollar behaved differently during the 1990 oil shock. Crude prices jumped 113% between June and October that year as a result of the Gulf War. The dollar, which was already in a downtrend because of Federal Reserve’s monetary easing, saw continued weakness this time as U.S. economic growth slowed.
Lien said the characteristics surrounding the oil price surge this time are more similar to the one in 1990 than those shocks of 1973 and 1979. “Therefore, it is easy to understand why the U.S. dollar has continued to weaken despite growing inflationary pressures,” she said.
The Federal Reserve has been consistently cutting interest and these rate cuts have played a far more dominant role in the price action of the dollar than the rise in oil, Lien said. “The market basically doesn’t believe that the Fed will start raising interest rates - and they have good reason to feel this way because based upon the last three oil shocks, growth in coming quarters should contract.”




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